This invention relates to a method for preparing haloformimine compounds. In particular, the present invention relates to an improved process for halogenation of formimine compounds.
Haloformimine compounds are a commercially important class of organic compounds. Haloformimines are useful as intermediates in the synthesis of a wide variety of organic compounds, such as microbicides, agricultural pesticides and pharmaceutical agents, such as antitumor agents. Certain haloformimines are also known as industrial bactericides.
Haloformimine compounds are typically prepared by reacting a carbonyl compound, such as glyoxylic acid, with an iminating agent, such as hydroxylamine, to form a formimine, followed by the addition of a base to the reaction mixture prior to reacting the formimine with a halogenating agent. For example, U.S. Pat. No. 4,879,314 (Hsu) discloses methods of preparing dihalooformaldoximes that require the addition of sodium bicarbonate to glyoxylic acid oxime before the halogenation step. The yield of dibromoformaldoxime by this method is only 46%. There is no discussion of maintaining the reaction at a specific pH during the halogenation step.
Such methods of preparing haloformimines typically result in low yields and the presence of significant levels of by-products. Much cost and effort must then be spent to purify the resulting haloformimine compound.
There is therefore a continuing need for a method of preparing haloformimine compounds that provides high yields and produces very low amounts of by-products.